In a wireless communication technology, when a Node B, for example, an Evolved Node B (eNB), sends data by multiple antennae, a data transmission rate may be increased in a space multiplexing manner, that is, a sender sends different data at different antenna locations by the same time-frequency resources, and a receiver, for example, User Equipment (UE), also receives the data by multiple antennae. As shown in FIG. 1, when a Node B is to send downlink data to terminals A, B, C and D in a cell, if an existing downlink transmission manner is adopted, the Node B needs to allocate different channel resources to A, B, C and D; and the Node B may adopt a Single User Multiple-Input Multiple-Output (SU-MIMO) manner to improve transmission efficiency. Under a single-user condition, resources of all antennae are allocated to the same user, the user is in possession of all the physical resources allocated by a Node B side in a transmission interval, and such a transmission manner is called SU-MIMO; while under a multiple-user condition, space resources of different antennae are allocated to different users, one user shares the physical resources allocated by the Node B side with at least one of other users in a transmission interval, a sharing manner may be a space division multiple access manner or a space division multiplexing manner, and such a transmission manner is called Multiple User Multiple-Input Multiple-Output (MU-MIMO), wherein the physical resources allocated by the Node B side refer to time-frequency resources.
In a Long Term Evolution (LTE) system, downlink physical Channel State Information (CSI) are reflected by three ways: a Channel Quality Indicator (CQI), a Pre-coding Matrix Indicator (PMI) and a Rank Indicator (RI).
A CQI is an index for determining quality of a downlink channel. In an existing technology, a CQI is represented by integral values from 0 to 15, representing different CQI levels respectively, different CQIs correspond to respective Modulation and Coding Schemes (MCSs), and there are totally 16 conditions which may be represented by 4-bit information.
A PMI refers to notifying an eNB of a pre-coding matrix for pre-coding a Physical Downlink Shared Channel (PDSCH) sent to UE according to measured channel quality in a closed loop space multiplexing sending mode only. Feedback granularity of the PMI may be feeding back the PMI in the whole bandwidth, or may also be feeding back the PMI according to sub-bands.
An RI is configured to describe the number of spatial independent channels, and corresponds to a rank of a channel response matrix. UE is required to feed back RI information in open loop space multiplexing and closed loop space multiplexing modes, and is not required to feed back the RI information in other modes. The rank of the channel matrix corresponds to the number of layers, so that the RI information fed back to an eNB by the UE is the number of the layers for downlink transmission.
A transmission layer has the meaning of “layer” under a multi-antenna condition in LTE and Long Term Evolution-Advanced (LTE-A), and represents the number of available independent channels in space multiplexing. The total number of transmission layers is a rank of a spatial channel. In an SU-MIMO mode, resources of all antennae are allocated to the same user, and the number of layers for transmitting MIMO data is equal to the rank adopted for transmitting the MIMO data by the eNB; while in an MU-MIMO mode, the number of layers for transmission of one user is smaller than the total number of the layers for transmitting the MIMO data by the eNB, and the eNB is required to notify different control data to the UE in different transmission modes for switching between the SU-MIMO mode and the MU-MIMO mode.
In a practical communication system, a Node B may adopt multiple transmitting and receiving antennae, while there may usually not be many antennae configured on a terminal of a user side under the limits of a factor such as a size and cost of the terminal, which may cause incomplete utilization of advantages of a MIMO technology.
An uplink virtual MIMO method disclosed at present is to combine multiple users to form virtual MIMO channels in the same time-frequency resource to jointly send data to a Node B with multiple antennae. When distances between the users are large enough, the channels for different users to reach the Node B may be considered to be uncorrelated, so that issue related to the size and the cost is addressed.
Virtual MIMO is divided into cooperative virtual MIMO and non-cooperative virtual MIMO. A main thought of cooperative virtual MIMO is that data may be shared between users and the antennae of respective users are shared to form a virtual multi-antenna system, and an existing uplink cooperative virtual MIMO technology mainly realizes a diversity function of MIMO; and non-cooperative virtual MIMO refers to that users may not share data but send independent data streams to a Node B respectively, the Node B selects some users for pairing according to channel conditions of the users, the paired users send data to the Node B in the same time-frequency resource, and the Node B distinguishes different users through multiple antennae, which is similar to that of downlink MU-MIMO, and non-cooperative virtual MIMO mainly realizes a multiplexing function of MIMO.
A virtual MIMO technology at the present stage is usually suggested for an uplink for a mobile terminal to send data to a Node B, and a non-cooperative manner is mainly adopted.
Device to Device (D2D) communication is a technology for direct communication between terminals, and its main characteristic is that: a certain device in multiple close devices covered by a network may find other devices in a wireless manner and realize direct connection and communication with the other devices. In D2D communication, resources are shared with cell users under the control of a cell network, so that a utilization rate of a frequency spectrum may be increased. In addition, D2D communication also has the advantages of: reducing a burden of a cellular network, reducing power consumption of a battery of a mobile terminal, increasing a bit rate, improving robustness of a failure of a network infrastructure and the like, and further supporting novel small-scale point-to-point data service.
Downlink virtual MIMO may allow sharing of receiving antennae of multiple users to form a virtual SU-MIMO receiver, and because of less interlayer interference, SU-MIMO may achieve higher link performance and higher downlink throughput compared with MU-MIMO, which is great for improving a communication condition of a hot spot with densely distributed users. However, downlink virtual MIMO is essentially cooperative virtual MIMO, and the terminals are required to share information received from a Node B and jointly perform demodulation and decoding. Since an existing mobile communication network architecture does not support data sharing between users, two processes are required for data interaction between users: 1, each user sends data to a Node B through an uplink channel respectively; and 2, the Node B forwards the data to the users in downlink channels. In such interaction processes, the antenna data may not be effectively shared between the users, so that an existing downlink virtual MIMO technology is not taken full advantage in a mobile communication system.
For the problem of incapability of an existing mobile communication network in effectively supporting a downlink virtual MIMO technology, there is yet no effective solution.